1. Field of the Invention
This invention relates to a heat-insulating swirl chamber engine equipped with main nozzles and subsidiary nozzles in swirl chambers.
2. Description of the Prior Art
It is known conventionally that when pre-mixture is sucked to a certain extent and the sucked premixture is compressed and is then injected from nozzles in a Diesel engine, the engine output is improved and the occurrence of smoke or the like is reduced. In this case, since the pre-mixture has an extremely lean mixture ratio and is distributed substantially uniformly throughout the cylinders, the pre-mixture existing near the cylinder wall and in the gap between the top land of a piston head and a cylinder liner is not burnt but is exhausted as an unburnt gas and results in deterioration of hydrocarbon components of a fuel, even after the fuel is injected from ordinary nozzles and burnt.
The structure of a heat-insulating engine utilizing a ceramic material as a heat-insulating material or as a heat-resistant material is disclosed, for example, in Japanese Patent Laid-Open No. 33454/1990. In the heat-insulating piston structure described in this reference, a main combustion chamber composed of a high density ceramic thin sheet and fitted to a cylinder head through a heat-insulating material is allowed to communicate with a subsidiary combustion chamber having a structure wherein its swirl chamber block is made of a material having low thermal conductivity, the inner wall surface of this swirl chamber block is made of a high density ceramic thin sheet and fuel injection nozzles are provided. In this heat-insulating engine structure, moreover, the main combustion chamber comprises a unitary structure of a head lower surface thin sheet made of a high density ceramic and opposing the lower surface of the cylinder head and a liner thin sheet, the liner thin sheet is fitted to the upper part of the cylinder liner made of a material having low thermal conductivity, inlet/outlet passages of the subsidiary combustion chamber are allowed to communicated with openings formed in the head lower surface thin sheet and the portion of the piston head on the main combustion side is composed of a high density ceramic head thin sheet.
In the heat-insulating engine structure disclosed in the above-mentioned Japanese Patent laid-Open No. 33454/1990, the thermal capacity of the ceramic members constituting the wall surfaces of both the main and subsidiary combustion chambers is reduced as much as possible so as to improve suction efficiency of the engine, mixing of the atomized fuel with air is rapidly effected due to the improvement in suction efficiency and moreover, a fuel equivalent ratio is drastically reduced in order to shorten the combustion time in a smoke generation temperature zone, to avoid combustion in the NOx generation temperature zone, to prevent the generation of the smoke and NOx and to prevent deterioration of strength resulting from the reduction of the thickness of the ceramic material.
However, the heat-insulating engine described above involves the problem of how the heat-insulating swirl chamber engine be constituted in order to recover the heat energy from the inner wall of the swirl chambers, to prevent diffusion of the lean mixture into the cylinders, to eliminate deterioration of hydrocarbons, to attain combustion inside the swirl chambers under the fuel-rich state to restrict the occurrence of NOx and to improve cycle efficiency by shortening the main combustion period.